Research Journal of Recent Sciences _________________________________________________ ISSN 2277-2502 Vol. 1(8), 64-66, August (2012) Res.J.Recent Sci. International Science Congress Association 64 Short Communication Electronic Properties of Ternary Compound Semiconductors Pal Naresh, Singh Sanjay, Hans Divya and Verma A.S.4 School of Applied Sciences and Social Sciences, Singhania University, Jhunjhunu, INDIA Department of Physics, Shyam Lal College, Delhi University, Delhi, INDIA Department of Physics, Ganjdundwara (P.G.) College, Ganjdundwara, INDIA Department of Physics, Panjab University, Chandigarh, INDIA Available online at: www.isca.in Received 6th April 2012, revised 19th April 2012, accepted 25th April 2012Abstract The description of crystal ionicity developed by Phillips and Van Vechten has been successfully employed in a wide range of semi-conductors and insulators. However, the applicability of this Phillips and Van Vechten (PV) dielectric analysis has been limited to only the simple A8-N compounds, which contain only one type of bond. Levine has extended the theory of PV to multi bond and complex crystals. Levine’s theory of ionicity has been used to calculate the various bond parameters for the chalcopyrites. In this paper a simple method based on the high frequency dielectric constants of solids, is proposed for the calculation of crystal ionicity (f) of chalcopyrite (AIIIVI and AIIIV) semiconductors. Our evaluated values are in excellent agreement with the values reported by different researchers. Keywords: Crystal ionicity, dielectric constants, chalcopyrites. Introduction Structurally chalcopyrite compounds are derived from that of the binary sphalerite structure (III-V and II-VI) with a slight distortion. Therefore, like binary compounds they have a high non-linear susceptibility. However because of the presence of two types of bonds in chalcopyrites they become anisotropic. This anisotropy gives rise to high bifringence. High non-linear susceptibility coupled with high bifringence in these compounds makes them very useful for efficient second harmonic generation and phase matching.During the last few years1-12, frequent attempts have been made to understand the electronic, mechanical, elastic and optical properties of chalcopyrite (AIIIVI and AIIIV) semiconductors. This is because of their interesting semi-conducting properties and various practical applications in the field of non-linear optics, electronics, photovoltaic detectors, light emitting diodes and solar cells etc. The concept of crystal ionicity of chemical bonding has been proved to be very useful in the characterization of molecular and solid state properties and there exist many ionicity scales proposed to correlate with a wide range of chemical and physical properties such as elastic constants, cohesive energy, heat of formation, bulk modulus, crystal structure etc13. Phillips and Van Vechten14-16, Levine13 and several other researchers17-21 have developed various theories and calculated ionicity for the case of simple compounds. In practice these theories require elaborate computation, and have been developed only for the limited semiconductors. Therefore, we thought it would be of interest to give an alternative explanation for the crystal ionicity (f) in chalcopyrite (AIIIVI and IIIV) semiconductors. In the proposed relation only one parameter such as the high frequency dielectric constant is required as input, to evaluate crystal ionicity of these compounds and the method turns out to be widely applicable.Material and Methods The average energy gap can be separated into the homopolar and the heteropolar parts according to the following relations14-16 = E + E (1) = E / E (2) = 39.74 / d2.48 (3) = 14.4b (Z / r) – (n/m) (Z/r-K r(4) Where E is the average energy gap of a crystal; f is the fractional ionicity; d is the nearest-neighbor distance (bond length), E the heteropolar part of average energy gap for Acompounds, b the pre-screening factor, e-K rthe Thomas-Fermi screening factor, and r = d/2. The numerical factors in equations (3) and (4) and the following ones are given for d expressed in Å and energy in eV. The most generalized form of the above equations has been discussed by Levine [13] in detail. The equations given by Levine reduce to those of PV when only one type of bond is present in the crystal. According to the Penn model17, the average energy gaps (E) for a semiconductor is given by, (E=Penn gap) (5) Research Journal of Recent Sciences ______________________________________________________________ ISSN 2277-2502Vol. 1(8), 64-66, August (2012) Res. J. Recent Sci. International Science Congress Association 65 Where is the valence electron plasmon energy and S is the quantity very near to unity and is responsible for the correction to bond model due to banding effect. The valence electron plasmon energy is given by10, eff8.28 (6) Where d and M are density and molecular or atomic mass respectively of material and neff is the effective number of valence electron. According to Tubb’s22, the crystal ionicity of a system is defined in terms of average energy gap E or Penn gap and Plasmon energy gap by the following relation, (7) After solving the relations (5) and (7) crystal ionicity may be calculated by the following relation, (8) Here is the high frequency dielectric constant. S is the constant and equal to unity. Results and Discussion Using equation (8), crystal ionicity (f), for chalcopyrite (AIIIVI and AIIIV) semiconductors has been calculated. The results are presented in table 1 and 2. The calculated values are in fair agreement with the values reported by Levine13 and V. Kumar23-25. Table-1 Values of crystal ionicity of AIIIVI chalcopyrite semiconductors Solids ee¥¥[26] [27] f [13] f [This work] CuAlS 2 5.95 0.69 00 0.45 CuAlSe 2 6.59 0.69 00 0.42 CuAlTe 2 7.55 0.71 00 0.39 CuGaS 2 6.23 0.69 0.70 0.44 CuGaSe 2 6.83 0.70 0.67 0.41 CuGaTe 2 7.67 0.71 00 0.39 CuInS 2 6.95 0.70 0.71 0.41 CuInSe 2 7.09 0.70 00 0.41 CuInTe 2 8.16 0.71 00 0.37 AgAlS 2 6.52 0.70 00 0.43 AgAlSe 2 7.13 0.70 00 0.40 AgAlTe 2 8.13 0.71 00 0.37 AgGaS 2 6.63 0.70 0.72 0.42 AgGaSe 2 7.22 0.70 0.71 0.40 AgGaTe 2 8.16 0.71 00 0.37 AgInS 2 7.03 0.70 00 0.41 AgInSe 2 7.7 0.71 0.73 0.39 AgInTe 2 8.74 0.72 00 0.36 Table-2 Values of crystal ionicity of AIIIV chalcopyrite semiconductors Solids ee¥¥[26] [27] f [13] f [This work] ZnSiP 2 10.51 0.36 0.28 0.32 ZnGeP 2 11.18 0.36 0.33 0.31 ZnSnP 2 12.78 0.37 0.38 0.29 ZnSiAs 2 11.43 0.37 0.33 0.31 ZnGeAs 2 11.99 0.37 0.31 0.30 ZnSnAs 2 13.53 0.37 0.29 0.28 CdSiP 2 10.45 0.37 0.37 0.33 CdGeP 2 11.19 0.37 0.38 0.31 CdSnP 2 12.79 0.37 0.42 0.29 CdSiAs 2 11.41 0.37 0.39 0.31 CdGeAs 2 12.13 0.37 0.37 0.30 CdSnAs 2 13.69 0.37 0.35 0.28 Conclusion The proposed empirical relation has been applied to evaluate crystal ionicity (f), of chalcopyrite (AIIIVI and AIIIV) semiconductors. We come to the conclusion that dielectric constanst of any compound is very important parameter for calculating the physical properties. It is also note worthy that the proposed relations are simpler widely applicable and values are in better agreement with reported data as compared to empirical relation proposed by previous researchers. The method presented in this work will be helpful to the material scientists for finding new materials with desired crystal ionicity (f), among the series of structurally similar materials.AcknowledgementOne of the authors (Dr. Ajay Singh Verma, PH/08/0049) thankful to University Grant Commission, New Delhi, India, for supporting this research under the scheme of U. G. C. Dr. D. S. Kothari Post Doctoral Fellowship. 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